New electric vehicles are typically supplied with a portable charging unit that allows the vehicle to be charged from a standard household electric outlet. The standard outlet typically is rated to supply 15 or 20 amps. The portable charging unit is commonly referred to as a portable EVSE (Electric Vehicle Service Equipment). The portable EVSE typically includes a handle and is adapted to provide for charging the battery of the electric vehicle at both the residence of the electric vehicle operator and at standard outlets remote from the residence.
The portability feature which allows and encourages the portable EVSE be plugged into a standard outlet also potentially presents significant risks. The integrity of the electrical connection at a standard outlet is extremely important for the charging of the electric vehicle since the battery charging commonly takes place over several hours. In some instances, a defective outlet could cause extreme heating and potentially lead to an electrical fire. The purpose of the present disclosure is to address the safety issues presented by defective standard outlets which are employed to supply power to EVSE.
When an electric vehicle is being charged it draws a very substantial current. Typically 80% of the outlet rating is drawn. For a 15 amp rating outlet current, 12 amps would be drawn. This high current load complies generally with all electrical codes. However, the rating is for electrical branch circuits with secure wire junctions of high electrical and mechanical integrity. Over time and through usage, an outlet rating is compromised, for example, by loose screws at the breaker or outlet, loose wires at the connection and worn outlet connectors. Such defective connections, which partially connect, and rarely do not completely not connect, to an appliance, cause a substantial voltage drop across the loose junction. The voltage drop multiplied by the current drawn through the junction results in a power dissipation which generates an elevated temperature at the junction.
For most conditions of usage of a standard outlet, using a household electrical appliance or device, such as, for example an electric drill, the voltage drop goes unnoticed and is rarely consequential because power is supplied intermittently and randomly. For short time periods, the generated heat from the loose wire junctions has ample time to dissipate.
The situation can be dramatically different when a portable EVSE is plugged into a standard outlet which has a loose wire, a loose circuit component and/or a loose connector at the outlet. This is because when the electric vehicle is charging, the current is continuously being drawn at a high level through the inlet over a long period of time. For some electric vehicles the charging may take place over 10-12 hours. Consequently, the power loss due to the defective electrical outlet and/or circuit will generate heat over an extended period of time. If heat is in the vicinity of easily ignitable material or flammable materials, a very dangerous situation will develop.
The use of auxiliary extension cords is also problematic. Each portable EVSE and/or electric vehicle is provided with a warning label or sheet indicating that the portable EVSE should not be used with an extension cord. Not all operators will pay attention to the warning label, and other individuals not knowledgeable of the extension cord advisory may be tempted to use an extension cord for convenience purposes. Extension cord connectors commonly wear and degrade. The usage of an extension cord introduces another structure where a substantial voltage drop could result in sufficient heat generated by the power loss to potentially cause a fire and represent a threat to property and personal safety.